The present invention is directed, in general, to a process for the preparation of taxol and other taxanes, and in particular, to such a process in which the C(7) or C(10) hydroxyl group of a taxane is selectively derivatized.
10-DAB (1), which is extracted from the needles of taxus baccata L., the English yew, has become a key starting material in the production of taxol and Taxotere, both of which are potent anticancer agents. Conversion of 10-DAB to taxol, Taxotere.RTM. and other taxanes having antitumor activity requires protection or derivatization of the C(7) and C(10) hydroxyl groups followed by esterification of the C(13) hydroxyl group to attach an appropriate side chain at that position. ##STR1##
Until now, strategies for the preparation of taxol and taxol analogs were based upon the observation of Senilh et al. (C.R. Acad. Sci. Paris, II, 1981, 293, 501) that the relative reactivity of the four hydroxyl groups of 10-DAB toward acetic anhydride in pyridine is C(7)--OH&lt;C(10)--OH&lt;C(13)--OH&lt;C(1)--OH. Denis, et. al. reported (J. Am. Chem. Soc., 1988, 110, 5917) selective silylation of the C(7) hydroxyl group of 10-DAB with triethylsilyl chloride in pyridine to give 7-triethylsilyl-10-deacetyl baccatin (III) (2) in 85% yield. Based upon these reports, in those processes in which differentiation of the C(7) and C(10) hydroxyl groups is required (e.g., preparation of taxol from 10-DAB), the C(7) hydroxyl group must be protected (or derivatized) before the C(10) hydroxyl group is protected or derivatized. For example, taxol may be prepared by treating 10-DAB with triethylsilyl chloride to protect the C(7) hydroxyl group, acetylating the C(10) hydroxyl group, attaching the side chain by esterification of the C(13) hydroxyl group, and, finally, removal of protecting groups.
It is known that taxanes having various substituents bonded to either the C(10) or the C(7) oxygens show anticancer activity. To provide for more efficient synthesis of these materials, it would be useful to have methods which permit more efficient and more highly selective protection or derivatization of the C(10) and the C(7) hydroxyl groups.